The best food-safe finishes are a matter of controversy among the experts. Finishes are often divided into film-forming finishes and penetrating finishes. Depending upon the area being covered and the type of food preparation being completed, a person would be wise to choose carefully.
History of Polyurethane
Professor Otto Bayer discovered polyurethane in the 1930’s while searching for a replacement for natural rubber. During that time period, the cost of rubber was high. Many people praise this accomplishment because they believe it is a compound that is better than rubber or any other replacement.
Polyurethane comes in many ranges according to flexibility and toughness. Less dense and flexible polyurethane is resistant to water and chemicals. This type is used in upholstery. Stiff polyurethane is used for thermal insulation.
Children’s Projects that Come in Contact with Food
Varnish, lacquer, boiled linseed oil, and shellac are said to be safe for children’s projects. Allow time for complete curing because this process takes longer than drying which will ensure safety. Some types of finish will cure by evaporation of the solvent. Others cure by reacting with oxygen.
The label on your container should give directions as to how long the curing process will take. Some bowls will require three days of curing after finishing is complete. There is a brushing lacquer that recommends seven days of curing before use. Since humidity, temperature, and application thickness can affect the curing process, it might be we wise to add a few days to any finished item.
Some experts do not recommend the use of polyurethane to finish children’s dishes, but others say that polyurethane is safe providing that the curing process has been sufficiently completed. Polyurethane has been said to hinder growth and development and even cause cancer in children. Of course, the problem was direct exposure to the fumes before the curing process was complete.
Possible Effects to the Body
Isocyanates are in polyurethane. Some Scientists believe isocyanates bring irritation to the lungs causing asthma attacks, bronchitis, colds, and other breathing issues. Brain cell swelling can be caused by isocyanates. Experts do not recommend that pregnant women and children be exposed to the fumes of polyurethane. Scientists also believe that workers who are exposed to polyurethane fumes for long periods of time will have digestive issues as well as lung irritation.
If you are interested in learning more about what woods you can safely keep in your home, take a look at the article I wrote “Can I use pressure treated wood in my home?”
Ways to Avoid Inhaling Polyurethane
People who work with polyurethane should be in a well-ventilated area when using it. Doors and windows should be kept open. When possible, stay away from areas where polyurethane fumigation is being done.
The Food and Drug Administration considers certain types of polyurethane safe for use on food surfaces. If the polyurethane forms a hard film, it is safe to use. The FDA advises everyone to wait for the surface in question to be dried and cleaned before being used for food preparation.
Pros and Cons of Polyurethane
The advantages of using polyurethane are as follows:
- It gives wood a beautiful look, and it provides protection.
- Wood usually shines after polyurethane applications.
- Surfaces are not easily scratched or damaged when finished with polyurethane.
The disadvantages of using polyurethane are as follows:
- The finish takes a long time to complete because it is in liquid form which causes it to have to be brushed rather than sprayed.
- The drying process takes longer than other finishes.
- It must be used in a well-ventilated area because it can cause irritation to the lungs in its liquid form.
Some experts recommend the use of conversion varnishes. They give a dark look to the wood. Many people who have used conversion varnishes on kitchen cabinets claim that it gives their cabinets a custom look that most people prefer.
One of the advantages of using a conversion varnish is that the drying process is quick. When the demand for product is high, quick drying time is a plus. Your product can be stacked and presented quickly and efficiently.
Another advantage to conversion varnish is that it has good mechanical strength. The pot life is long, and the solid percentage is high. Customers often look for these qualities when shopping for wood products.
Although conversion varnishes are often considered more food-safe, there are some disadvantages to their use. Limited chemical resistance, instability when exposed to ultra violet rays, and touch-up difficulty are just a few cons to using these types of varnishes. Formaldehyde content has been used in many conversion varnishes which could possibly pose more of a danger than polyurethane.
Other Safety Concerns
Some wood experts have expressed concern with the use of certain utensils with polyurethane finished dishes. A few experts have indicated that scratching of the wood by utensils could present a hazard if the bowl is reused.
An even greater concern is raised with the use of polyurethane on cutting boards where there is a high risk of scratching to the wood. Experts believe that chemicals could possibly seep from damaged wood into food. A penetrating oil finish is recommended on wood that could be damaged by scratching from utensils or other objects.
Another concern raised by experts is that of certain finishes, including polyurethane, on dining room tables. According to some wood workers, all types of wood finishes can only stand so much heat exposure. Hot plates, pots, and pans can bring damage that could cause chemical seepage if not properly treated.
Guaranteed Food Safe Finishes
There are some finishes that most experts agree as to the safety of use with food preparation. Some of these are pure tung oil, raw linseed oil, mineral oil, walnut oil, beeswax, carnauba wax, and certain shellac. For a list of specific food safe finishes that I recommend, please take a look at this page.
Pure tung oil is extracted from the nut of the China wood tree. It is available in most hardware stores and catalogs. The disadvantages to using pure tung oil are that it is difficult to apply and requires many coats.
Raw linseed oil is pressed from flax seeds. It is listed as a food additive by the Food and Drug Administration. The disadvantage to using raw linseed oil is that it requires long curing time, has low water resistance, and must be reapplied frequently.
Although mineral oil is derived from petroleum, it is inert, colorless, tasteless, and odorless. Mineral oil is simple to apply, but it has low water resistance. It also requires frequent reapplication.
Walnut oil comes from nuts on a walnut tree. It is sold both in grocery stores and health food stores as salad oil. Although walnut oil is easy to apply, it does require frequent reapplication.
Beeswax, which comes from the honey bee, can be mixed with oil to create a water-resistant finish. Beeswax can be found in most wood working catalogs.
Carnauba wax comes from the Brazilian palm tree. It is more water resistant than Beeswax. Carnauba wax can be used on woodenware, or, as a top-coat polish. It is sold in most woodworking catalogs.
Shellac is secreted from the lac bug and harvested in India. The most water-resistant variety is super blond shellac. It is sold in woodworking, art, and hardware supply stores and catalogs. I really like the Old World Shellac brand and you can pick it up here on Amazon for a very reasonable price. I’ve had great success with it.
Polyurethane or Not?
While some experts argue that polyurethane and other wood finishes are food-safe once they have completed the curing process, others have concerns about chemicals seeping from scratched surfaces. Although it can be confusing, using any dish or cutting board that has been finished with polyurethane should be approached with caution.
It is vital for people to have the facts. After the facts have been presented, it is up to the customer to decide what is best. Caution should always be the order of the day.